The present invention relates to an information memory device and a data processing apparatus which offer a high level of security. In addition, the present invention relates to a card and an information processing system. In particular, the card is typically represented by an IC card (smart card) which includes an embedded single-chip CPU (Central Processing Unit) serving as an information processing device.
In a microcomputer chip offering a high level of security such as the representative IC card, data to be kept confidential may be encrypted and decrypted by using a key for encryption. The key for encryption is a kind of secret information or information which can not be rewritten as one pleases.
As shown in FIG. 1, the basic configuration of a microcomputer comprises a central processing unit 8001, a memory device 8002 and a signal line 8003 serving as a path used by a variety of components for exchanging information. The central processing unit 8001 carries out logic and arithmetic processing. The memory device 8002 is implemented typically by using memories such as a ROM (Read Only Memory), a RAM (Random Access Memory), an EEPROM (Electrical Erasable Programmable Read Only Memory) and a FRAM (Ferromagnetic Random Access Memory). A ROM is a memory, data stored in which can not be changed. A ROM is used mainly for storing a program. On the other hand, a RAM is a memory, data stored in which can be rewritten with a high degree of freedom. When power supplied to the RAM is turned off, however, data stored therein is deleted. Thus, when power supplied to an apparatus employing the microcomputer is interrupted, data stored in the RAM disappears. On the other hand, an EEPROM and a FRAM are each a memory capable of holding data stored therein even if power supplied thereto is cut off.
A typical main unit of a computer provided in a contact IC card is shown in FIG. 2. The figure shows only a pin layout of a semiconductor-device chip 51. The main unit of the computer is a chip called a COT (Chip on Tape) placed at the center of the card. It should be noted, however, that the main unit is generally called a module. The layout of pins shown in the figure is a typical pin layout. That is to say, the IC card has a Vcc (power supply) pin, a GND (ground) pin, an RST (reset) pin, an I/O (input/output) pin and a CLK (clock) pin. The chip is driven to operate by signals supplied to the pins from typically a terminal. It should be noted that, as the terminal itself, an ordinary card system capable of sufficiently providing necessary functions can be employed. The amount of power consumed by the chip can be measured by observing signals at the Vcc and GND pins. The measurement of the power consumption is described in Section 8.5.1.1 Passive Protective Mechanisms on Page 263 of a reference with a title of “Smart Card Handbook” authored by W. Rankle and W. Effing and published by John Wiley & Sons in the year of 1997.